I. Field of the Invention
The present invention relates to a process and a device for remote transmission of signals and the application of this process and device to the detection and/or measurement of the amount of combustible gas in an atmosphere.
II. Description of the Prior Art
Transmission of power to a remotely located sensor by means of a line which also provides both the transmission of an interrogation signal to that sensor and data signals from that sensor is known. One such process and device is described in French Pat. No. 2,350,461. The process and device described therein provides a power supply signal to a remotely located sensor by means of conveying a direct current in a line which connects that sensor to a central station, such as a central processing unit. This process and device sends an interrogation signal from the central station to the sensor in the form of a direct current signal on that line, which direct current signal is of reverse polarity to the direct current signal used to power the sensor. If it is desired to supply a multiplicity of sensors by means of a single line, such prior art processes and devices cannot supply the line with an adequate amount of direct current due to the intrinsic power consumption of the sensors and the limit on the amount of direct current which can be applied to the line in view of the safety hazards a high amount of direct current presents.
It is, accordingly, a primary object of the present invention to provide a process and device for remote transmission of signals issued by at least one sensor to a central station, which sensor is supplied by power over a remote transmission line, and wherein the power necessary to adequately supply that sensor and preferably even the power necessary to operate electronic circuits with which the sensor is associated, is transmitted by the line.
Another object of the present invention is to provide such a process and a device which fulfills the triple function of supplying power to the sensor and preferably to the circuits associated with that sensor, of transmitting interrogation signals to that sensor, and of transmitting data signals from that sensor to a central station.
Another object of the present invention is to provide such a process and device in which the transmission line can transmit interrogation signals to, and data signals from, at least one sensor which is not supplied with power from that line.
A still further object of the present invention is to make possible the powering of remotely located sensors (more particularly to ensure adequate charging of batteries which operate to power such sensors) by means of a low current intensity signal on the transmission line.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.